Plasma display panels (hereinafter, PDPs), which are characterized by high definition and large screen size, have been commercialized as 100 inch class televisions and other products. In recent years, PDPs are planned to be used in high-definition televisions having more than double the number of scan lines than conventional NTSC televisions. There is also an increasing demand for lower power consuming and lead-free PDPs in terms of energy and environmental issues.
A PDP basically includes a front panel and a rear panel. The front panel includes a glass substrate, display electrodes, a dielectric layer, and a protective layer. The glass substrate is a sodium borosilicate glass produced by a float process. The display electrodes consist of transparent electrodes and bus electrodes arranged in a stripe pattern on a main surface of the glass substrate. The dielectric layer coats the display electrodes and functions as a capacitor. The protective layer is made of magnesium oxide (MgO) and formed on the dielectric layer.
The rear panel, on the other hand, includes a glass substrate, address electrodes, an underlying dielectric layer, barrier ribs, and phosphor layers. The address electrodes are arranged in a stripe pattern on a main surface of the glass substrate. The underlying dielectric layer coats the address electrodes. The barrier ribs are formed on the underlying dielectric layer. The phosphor layers, which emit red, green, and blue light, are formed between the barrier ribs.
The front and rear panels are air-tight sealed with their electrode bearing sides opposed to each other, and have a discharge space partitioned by barrier ribs and filled with a discharge gas of neon (Ne) and xenon (Xe) at a pressure of 400 to 600 Torr (50000 to 80000 Pa). In the PDP, the display electrodes are discharged by selectively applying a video signal voltage thereto, and the discharge generates ultraviolet light, which excites and illuminates the red, green, and blue phosphor layers, thus achieving color image display.
A general method for driving such a PDP includes an initializing period, an address period, and a sustain period. In the initializing period, wall charges are adjusted to facilitate an address discharge. In the address period, an address discharge is generated according to an input image signal. In the sustain period, display is performed by generating a sustain discharge in a discharge space in which the address discharge has been generated. These periods are combined to form a period (subfield), which is repeated a plurality of times in a period (one field) corresponding to one image exposure, thereby achieving gradation display of the PDP.
In such a PDP, the role of the protective layer on the dielectric layer of the front panel includes protecting the dielectric layer from ion impact caused by discharge and emitting initial electrons for generating an address discharge. The protection of the dielectric layer from ion impact is important to prevent an increase in the discharge voltage, whereas the emission of initial electrons for generating an address discharge is important to prevent address discharge failure, which results in image flicker.
In order to reduce image flicker by emitting a larger number of initial electrons from the protective layer, it has been suggested to make a magnesium oxide (MgO) protective layer have impurities therein or have magnesium oxide (MgO) particles thereon (see, for example, Patent Literature 1, 2, 3, 4, and 5).
Televisions are becoming higher in definition in recent years, and there is a growing demand on the market for low-cost full HD (high-definition) PDPs having high resolution (1920×1080 pixels: progressive display), low power consumption, and high luminance. It is extremely important to control the electron emission performance of the protective layer because it determines the image quality of the PDPs.
Displaying higher definition images requires a larger number of pixels to be addressed although one field time is the same, thereby requiring that a pulse to be applied to the address electrodes in the address period of each subfield should have a smaller width. However, there is a time lag called a “discharge delay” after a voltage pulse rises and until a discharge occurs in the discharge space. As a result, the small pulse width provides a low probability of completing the discharge in the address period, thereby reducing image quality such as lighting failures and flickers.
In order to improve the efficiency of emission caused by discharge so as to achieve lower power consumption, it is possible to increase the xenon (Xe) partial pressure. This, however, increases the discharge voltage and the discharge delay, thus reducing the image quality such as lighting failures.
Thus, providing a PDP with higher definition and lower power consumption requires maintaining a low discharge voltage, and at the same time, preventing lighting failures so as to keep high image quality.
The approach of improving electron emission performance by adding impurities to the protective layer, however, causes electric charges to decrease at a higher rate when accumulated on the protective layer surface so as to be used as memory. This requires, for example, increasing the applied voltage to compensate such a decrease in the electrification.
In the approach of providing magnesium oxide (MgO) crystal grains on the magnesium oxide (MgO) protective layer, on the other hand, lighting failures can be reduced by reducing the discharge delay, but the discharge voltage cannot be reduced.
In view of these problems, the present invention has an object of providing a PDP having high luminance display and capable of being driven with a low voltage.    Patent Literature 1: Japanese Patent Unexamined Publication No. 2002-260535    Patent Literature 2: Japanese Patent Unexamined Publication No. H11-339665    Patent Literature 3: Japanese Patent Unexamined Publication No. 2006-59779    Patent Literature 4: Japanese Patent Unexamined Publication No. H8-236028    Patent Literature 5: Japanese Patent Unexamined Publication No. H10-334809